The invention relates to power trains of motor vehicles in general, and more particularly to improvements in methods of and in apparatus for operating adjustable torque transmitting systems (e.g., in the form of engageable and disengageable friction clutches) of such power trains.
As a rule, or at least in many instances, the operation of the friction clutch in the power train of a motor vehicle (normally but not necessarily between the rotary output element of a prime mover and the rotary input element of a change-speed transmission) is regulated automatically by one or more actuators (e.g., electric motors in conjunction with gearings and/or fluid-operated cylinder and piston units) which receives or receive signals from a computerized control unit. The control unit normally processes signals denoting various operational parameters of the motor vehicle and/or of its power train; and its output signal to the actuator or actuators reflects the intensity or intensities (and/or other characteristics) of the signal or signals being processed by the evaluating circuit or circuits of the control unit.
An advantage of an automatically operated torque transmitting system (hereinafter called clutch or friction clutch for short) is that it contributes considerably to the comfort of the operator and other occupant(s) (if any) of a motor vehicle. Furthermore, the utilization of an automatically engageable and disengageable friction clutch can entail a reduction of fuel consumption, especially when the clutch is connected between the crankshaft or camshaft of an internal combustion engine (such as an Otto engine) and the input shaft of an automated or automatic transmission in the power train of a motor vehicle. Such types of power trains are more likely to ensure an automatic selection of a transmission ratio which is best suited for the transmission of torque to the driven wheels of the motor vehicle, namely which is most likely to ensure a highly economical operation of the engine under the prevailing circumstances of use of the motor vehicle.
In order to reduce the energy consumption of the associated actuator or actuators, as well as to ensure speedy adjustments of the magnitude of transmitted torque, an automated clutch is normally operated in such a way that the extent of its engagement is best suited for operation without slip or without undue (excessive) slip. To this end, it is customary to select the extent of engagement of the clutch as a function of the RPM of the rotary output element of the prime mover, of the RPM of the rotary input element of the transmission (such RPM is normally indicative (or it can be utilized for a determination) of the speed of the motor vehicle), and the load upon the prime mover in such a way that the clutch can transmit a predetermined torque.
However, when the circumstances of use of a motor vehicle depart from normal circumstances, for example, when the vehicle is utilized on mountain roads or elsewhere well above the sea level (turbo engines are particularly sensitive under such circumstances of use), when the outside temperature is very low, and/or under certain other circumstances, it can happen (especially while setting the vehicle in motion) that the disengagement of the clutch is excessive which prevents the engine from reaching an RPM at which it can or could furnish a maximum torque. This can prevent the engine from developing an adequate power during starting of the motor vehicle.
The RPM of a rotary input element of a manually shiftable, automated or automatic transmission (such as a continuously variable transmission known as CVT) can be ascertained on the basis of the transmission ratio and the rotary output element of the transmission (e.g., a shafty which drives the differential of the power train) or by resorting to suitable sensor means.